Storage of two liquids, or liquids of different densities, in a single storage tank is old and wellknown. Single tank storage may be advantageous for a number of reasons, including the reduction of facility costs and size. Such storage tanks, and the uses therefor, are shown in U.S. Pat. Nos. 3,438,215; 3,680,729 and 4,209,271.
Where it is desirable to prevent intermixing of the liquids, or to inhibit heat transfer between liquids at different temperatures within the tank, a means of mechanical separation of the liquids may be advantageously employed. Such mechanical separation may be accomplished by extending a peripherally fixed flexible membrane across the tank at the desired liquid interface. Alternately, a vertically movable deck may be utilized, which can accommodate large changes in the relative volumes of the liquids within the tank. Vertically movable separation decks are also shown in U.S. Pat. Nos. 3,438,215; 3,680,729 and 4,209,271.
As described in the prior art, the general construction of the storage tank and separation deck depend on a number of factors, including the densities of each of the two liquids, the degree of heat loss allowable through the tank walls, and the degree of heat loss and intermixing permissible between the two liquids.
A problem not addressed by the prior art concerns deck tilting or skewing. In the ideal situation, equally distributed frictional forces would exist around the periphery of the deck as a result of the sealing means between the deck and the interior of the tank. In addition, equally distributed buoyant and hydrostatic pressure forces would exist over the surfaces of the deck. In practice, however, the frictional forces around the periphery of the deck vary with irregularities at the seal, and buoyant forces vary with irregularities in the density of the deck as well as with uneven temperature distributions within the tank. These imbalanced forces may cause the separation deck to tilt or skew disadvantageously, rendering the mechanical separation barrier ineffective.